The overall goal of this proposal is to establish the regulation and function of sulfotransferase (SULT) 4A1 during development and in adults in the genetically tractable zebrafish (Danio rerio) model system. SULT4A1 is an orphan enzyme that has been included in the cytosolic SULT gene family based on its structural homology. SULT4A1 mRNA and protein are selectively expressed in neurons in the vertebrates examined. The function of SULT4A1 in the nervous system is of interest since the protein is greater than 98.5% identical in amino acid sequence in mammals and almost 90% identical in vertebrate species, including zebrafish. In humans, the SULT4A1 gene has been identified as a susceptibility gene for the occurrence of schizophrenia based on both transmission disequilibrium studies and its association with psychopathology. SULT4A1 gene deletion has also been linked to Phelps-McDermid syndrome, a generalized cognitive and developmental deficit syndrome. Recently our laboratory has reported that transient inhibition of SULT4A1 expression in zebrafish embryos is associated with the significant dysregulation of multiple genes in phototransduction. This is the first association of SULT4A1 with a physiological function. To date, no convincing evidence as to its substrate selectivity or activity has been identified for the enzyme in any species or following cell or bacterial expression and purification The high homology of zebrafish SULT4A1 to the enzyme in other vertebrates provides a valuable model system for the examination of its developmental and physiological regulation and function. Generation of both active site and knockout SULT4A1 mutants will be used to investigate the effects of its loss of activity on zebrafish development, behavior, vision and neuronal properties. TALENs have been utilized to generate both 5 AA active site deletion and frameshift knockout SULT4A1 mutants that survive to adulthood and breed as homozygotes. The SULT4A1 mutants provide a framework for developing a better understanding of the function and activity of SULT4A1 in zebrafish as elaborated by the following specific aims. Due to the high conservation many brain functions and properties in vertebrate evolution the zebrafish system will provide valuable insights into the role of SULT4A1 in human neurobiology. 1) To investigate the effects of disrupting SULT4A1 activity or expression on zebrafish development. Analysis of morphological characteristics of embryos and adults, gene expression, and reproduction will be carried out in the TALEN-derived SULT4A1 mutants. 2) To identify behavioral phenotypes in larval and adult SULT4A1 active site deletion and knockout zebrafish. Vision and behavioral studies will be performed to generate insights into the neural effects of SULT4A1 dysfunction. 3) To analyze the role of SULT4A1 in phototransduction in the zebrafish eye. Transient inhibition of SULT4A1 expression in zebrafish embryos resulted in the up-regulation of expression of multiple genes involved in phototransduction. Retinal function and signal transduction will be examined in the SULT4A1 mutants to identify affected neuronal pathways.